The invention relates to a an apparatus for measuring radiation emerging from an optical fiber, comprising a hollow body surrounded by diffusely reflecting walls into which the end of the optical fiber can be introduced, and at least one detector arranged behind an opening of the hollow body.
German Patent Document DE 29 50 124 C2 discloses a so-called power meter for high energy lasers, in which the end of an optical fiber is slid into the opening of a chamber with at least partially diffusely reflecting walls. The light which emerges from the optical fiber is focussed by means of a lens, and impinges first on a diffusely reflecting plate and, after further reflections, through openings in the plate, onto detectors disposed behind them. Between the openings in the diffusely reflecting plate and the detectors, a filter plate is arranged for the reduction of the radiation passing through.
Despite its symmetrical construction, it was found that this arrangement is relatively sensitive to changes in the entry angle of the radiation and the radiating characteristics of the optical fiber. The selection of the filter disk and its surface quality also present problems.
It is therefore an object of the present invention to provide a radiation meter of the above-mentioned generic type which is less sensitive to changes in the entry angle of the radiation and to the radiating characteristics of the optical fiber, and which can be manufactured at lower cost due to the fact that optical elements, such as lenses or filters are not required.
These and other objects and advantages are achieved according to the invention by applying the principle of the Ulbricht sphere, in which, in contrast to known apparatus (such as the German Patent Document DE OS 24 17 399), no optical elements, such as filters or lenses are used for coupling and reduction of the light. The device according to the invention has the additional advantage that it can easily be adjusted to different radiation intensity ranges without the changing filters or detectors.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.